Epidemiology of COVID-19 cases and vaccination coverage in Seremban District, Malaysia, 2021

Objective Malaysia’s first case of coronavirus disease (COVID-19) was reported in January 2020, with the first case in the state of Negeri Sembilan diagnosed on 17 February 2020. The National COVID-19 Immunization Programme commenced in early March 2021 in Negeri Sembilan. This study describes the COVID-19 cases and vaccination coverage in Seremban District, Negeri Sembilan, during 2021. Methods The demographic and clinical characteristics of COVID-19 cases and the district’s vaccination coverage were described. Vaccination coverage was plotted against COVID-19 cases on the epidemic curve. The χ2 test was used to examine the differences between the vaccination status of COVID-19 cases and severity category, hospitalization status and mortality. Results In Seremban District, there were 65 879 confirmed cases of COVID-19 in 2021. The data revealed that the  21–30-year age group had the highest proportion of cases (16 365; 24.8%), the majority of cases were male (58.3%), and most cases were from the subdistrict of Ampangan (23.1%). The majority of cases were Malaysian. Over half (53.5%) were symptomatic, with fever (29.8%) and cough (22.8%) being the most frequently reported symptoms. COVID-19 vaccination status was significantly associated with severity category, hospitalization and mortality (P < 0.001 for all categories). Discussion This is the first study to describe two-dose vaccination coverage and the trend in COVID-19 cases in Seremban District. It was observed that COVID-19 cases had been reduced following more than 60.0% vaccination coverage.

The number of COVID-19 cases per week increased between March and August 2021, declined in early August 2021, and then plateaued until December 2021. On 8 August 2021, two-dose vaccination coverage for adults reached 56% (Fig. 1).
There was a significant difference in the distribution of unvaccinated and vaccinated (two doses) cases by severity category, hospitalization and mortality (P < 0.001; greater than 10% OR a person (alive or dead) with a positive reverse transcription polymerase chain reaction test. 5 COVID-19 severity was classified into five categories: category 1, asymptomatic; category 2, symptomatic without pneumonia symptoms; category 3, symptomatic with pneumonia symptoms; category 4, requiring intensive care and supplemental oxygen; and category 5, critical illness with multiple organ involvement. 6 Telephone interviews for every case were conducted by employees of the Seremban District Health Office to gather data on demographics, symptoms, onset date, date of exposure, travel history, comorbidities and vaccination status. Vaccination coverage for Seremban District from March to July 2021 was obtained from data compiled manually in Microsoft Excel® from each health-care facility and the Malaysia Vaccine Administration System. From 23 July to 31 December 2021, vaccination coverage was obtained through an automated system. 7 Vaccination coverage was plotted against COVID-19 cases on an epidemic curve (Fig. 1).
All verified data were recorded in a line list, and Microsoft Excel® was used for data analysis. The demographic and clinical characteristics of confirmed COVID-19 cases and district vaccination coverage were tabulated and analysed using descriptive statistics. The chi-square test was used to examine the differences between the vaccination status of COVID-19 cases and severity category, hospitalization status and mortality.

RESULTS
There were 65 879 confirmed cases of COVID-19 in Seremban District in 2021, giving an incidence rate of 10 358 per 100 000 population. The cases were distributed unevenly among the eight sub-districts. Subdistrict Ampangan recorded the highest number of cases ( Our data showed that the number of COVID-19 cases per week was decreasing when two-dose vaccination coverage reached 60.0%. While vaccination has been shown to reduce COVID-19 outbreaks, 13,14 the impact of other response components also needs to be considered. Malaysia was under its third movement control order from 12 May 2021 to 1 April 2022, during which international, inter-state and inter-district travel, as well as economic, social, educational, sports and business operation hours, were restricted. Physical distancing and mask use were enforced nationwide under the Prevention and Control of Infectious Diseases Act 1988. Personal hygiene practices including hand washing were continuously promoted by the Ministry of Health through various media platforms. During this period, COVID-19 variants Alpha and Beta were mostly circulating in Malaysia before the Delta variant emerged in July 2021. 15 Another intervention for COVID-19 was the establishment of the Greater Klang Valley Special Task Force on 12 July 2021. This task force was a multi-agency collaboration for COVID-19 management in the Klang Valley (covering the federal territories of Kuala Lumpur and Putrajaya and the state of Selangor) and Seremban District. The task force's objectives included organizing strategic actions to improve health-care delivery, lessening the transmission of infectious diseases, and assisting both the general public and health-care professionals. 16 Table 3). The proportion of cases being hospitalized or dying who received two vaccine doses was lower compared to those who were unvaccinated ( Table 3).

DISCUSSION
This study describes the demographic and clinical characteristics of 65 879 cases of COVID-19 from the most densely populated district in the state of Negeri Sembilan. It demonstrated that the number of cases per week declined after the district vaccination coverage reached 60.0%.
The 21-30-year age group had the highest proportion of COVID-19 cases, possibly due to rapid housing development and a growing workforce in this district. 8 The fact that there were more cases among the male population could be due to their being less compliant with preventive measures such as frequent hand washing, face-mask use and stay-at-home orders. 9 The high proportion of cases registered among Malaysian nationals is most likely due to international travel restrictions. The high urbanization and population density in Ampangan sub-district 10 may also account for the elevated number of cases. Most COVID-19 cases were asymptomatic and detected through contact tracing. The high proportion of young cases may have contributed to the increased number of asymptomatic individuals, as younger individuals tend to have mild or no symptoms. 11 Compared to vaccinated cases, unvaccinated cases had higher proportions of cases in the higher severity categories, hospitalizations and deaths, similar to a previous study from Malaysia,  To our knowledge, this is the first study to describe two-dose vaccination coverage and the trend of COVID-19 cases in Seremban District. It was observed that COVID-19 cases decreased once 60.0% vaccination coverage had been reached. The strength of this study is in the use of large datasets acquired from the Seremban District Health Office, which may reflect the real number of COVID-19 cases in other districts. These data are managed systematically, making their source more reliable.
This study has limitations, the first of which is that it is a descriptive observational study of one area in Malaysia. A more sophisticated statistical analysis is needed to compare vaccination coverage and the number of COVID-19 cases. Given that only symptomatic patients were screened for COVID-19, 15 a potentially large number of individuals with asymptomatic infection may have remained undiagnosed, thus contributing to the lower number of reported COVID-19 cases. Other limitations include: the lack of data on disease progression and on the use of the severity categories during diagnosis; the unavailability of COVID-19 vaccine for the different variants; and the fact that case data on COVID-19 variants were not obtained during field investigations as they were not a priority for the primary management of COVID-19. The findings of this study need to be interpreted with caution.
In summary, this study describes the epidemiology of COVID-19 cases in 2021 in Seremban District, Malaysia. Although we show that the COVID-19 case COVID-19 cases and vaccination coverage in Seremban Khairul Amin et al  numbers decreased as vaccination coverage increased, other control measures such as movement control orders, physical distancing, mask use and regular hand washing are likely to have also contributed to the decrease in cases. Additional analyses are needed to confirm an association between COVID-19 cases and vaccination coverage.